Russia and China's veto of a UN Security Council resolution on Syria was a travesty, the United States said on Saturday, saying it would work with other nations to support democratic change in the Arab nation.

The resolution vetoed by Russia and China would have urged Syrian President Bashar Assad to give up power after a bloody 11-month uprising.

U.S. Secretary of State Hillary Rodham Clinton speaks during a press conference at the 48th Munich Security Conference in Munich, southern Germany, Feb. 4, 2012.AP

It also would have supported an Arab League plan under which Assad would have ceded powers to a deputy, withdraw troops from towns and started a transition to democracy.

U.S. Secretary of State Hillary Clinton pulled no punches in criticizing the vetoes by Russia and China, though she did not mention either by name.

"What happened yesterday at the United Nations was a travesty," she said.

Clinton told a joint news conference with Bulgarian Prime Minister Boiko Borisov during a brief visit to Sofia: "Those countries that refused to support the Arab League plan bear full responsibility for protecting the brutal machine in Damascus."

"Faced with a neutered Security Council, we have to redouble our efforts outside of the United Nations with those allies and partners who support the Syrian people's right to have a better future," she said. "We have to increase diplomatic pressure on the Assad regime and work to convince those people around President Assad that he must go."

Clinton also said the United States would work with other nations to try to tighten "regional and national" sanctions "to dry up the sources of funding and the arms shipments that are keeping the regime's war machine going."

"We will work to expose those who are still funding the regime and sending it weapons that are used against defenseless Syrians, including women and children," she said. "We will work with the friends of a democratic Syria around the world to support the opposition's peaceful political plans for change."

Clinton did not give further details which nations might band together or precisely what they might do, but it appeared that the United States might seek to organize a "Friends of Syria" group to act together given the inability to make progress at the United Nations because of Russia and China.

Saturday's 13-2 UN Security Council vote came a day after activists say Syrian forces bombarded the city of Homs, killing more than 200 people in the worst night of bloodshed of the conflict.

Russia said the resolution was biased and would promote "regime change". Syria is Moscow's rare ally in the Middle East, home to a Russian naval base and a customer for its arms.

The Syrian National Council, which represents major opposition groups, said it holds Moscow and Beijing "responsible for the escalating acts of killing and genocide; it considers this an irresponsible step that is tantamount to a license to kill with impunity".

The United Nations estimated late last year that at least 5,000 people had been killed in the conflict. And activists have reported hundreds of deaths since then. The Syrian government has said that 2,000 of its security forces have been killed in the violence.

If activists' accounts are accurate, the bombardment of Homs on Friday night was one of the bloodiest episodes of the Arab Spring uprisings sweeping the region and the deadliest incident in the Syrian conflict.

Syria's ambassador to the United Nations denied its forces killed hundreds of civilians in Homs, saying that "no sensible person" would launch such an attack the night before the Security Council was set to discuss his country.

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